Washington: The governor of the US state of Oklahoma has issued a last-minute stay of execution of an inmate convicted of ordering a murder, amid questions over one of the lethal injection drugs.

Richard Glossip -- whose case had sparked appeals for clemency from Pope Francis, celebrities and others -- had been set to die in the afternoon, following a two-week reprieve to allow time for the consideration of new evidence in his murder conviction.

But Republican Governor Mary Fallin issued a surprise 37-day stay yesterday, saying the state needed time to address questions about the use of potassium acetate in the three-drug lethal injection cocktail and ensure it complies with court-approved protocols.

"Last minute questions were raised today about Oklahoma's execution protocol and the chemicals used for lethal injection," Fallin said in a statement.

Her executive order said the stay was granted to allow time to check on the viability of the substitute drug, "and/or obtain potassium chloride," which is the drug normally used.

Oklahoma found itself in the midst of a firestorm last year over a botched execution that sparked a national and international outcry.

Glossip had challenged the legality of a different drug used in the state's lethal injection protocol before the Supreme Court -- one called into question in connection with last year's painful execution -- but lost that case.

He also had failed to secure a last-minute stay from the high court yesterday. It rejected an appeal from Glossip's lawyers without explanation.
Fallin's executive order came about an hour later.

The execution is now set for November 6.

Glossip was found guilty of recruiting fellow motel employee Justin Sneed to carry out the 1997 murder of owner Barry Van Treese.

He was subsequently convicted based on the testimony of Sneed, who pleaded guilty and was able to negotiate a life sentence by claiming his co-worker had masterminded the plot.

Glossip has long proclaimed his innocence, and his lawyers have repeatedly questioned Sneed's credibility.